I and II,

III and IV,

V and VI

Explanation:

Position isomerism means, where the length of the parent chain and functional group is same but the position of the functional group is different, then it is called position isomer. In case of( I and II ) the parent chain has 4 Carbons each. But the functional group –OH is on 1^st carbon in the 1^st compound and on 2^nd carbon in the 2^nd compound.In (V and VI) alsothe parent chain has 4 Carbons each. But the functional group –O- (ether) is placed between 2^nd and 3^rd carbon in compound V while the ether group is placed between 1^st and 2^ndcarbon in compound VI. In case of (III and IV) the parent chain has only 3 carbons(as it is branched), but the –OH group in compound III is on 1^st carbon while –OH group in compound IV is on 2^nd carbon. since they have the same chain length and same functional group but different positions for functional group.